Research On Related Techniques For Virtual Assembly System With Force And Haptic Feedback

Force and haptic feedback technology provides operators with the ability of feeling features,constraints and interactions of virtual models,which enables them to interact with virtual environment in real-time way.In order to make virtual assembly (VA) interaction more real,this dissertation studied VA technology based on force and haptic feedback taking PHANToM^? Desktop,which is a kind of force and haptic feedback device of single point type,as the force and haptic feedback device.Both the research contents and the research methods in this dissertation can act as references for the research and application using other force and haptic feedback devices of single point type.With the development of force and haptic feedback technology,VA technology based on force and haptic feedback is developed on the base of VA technology with no force and haptic feedback.Comparing with no force and haptic feedback one,the VA technology based on force and haptic feedback should study three additional issues, which are the force and haptic feedback interface oriented to VA operation,the interaction manners of VA based on PHANTOM device and the assembly operation and navigation based on force-feedback.At the beginning of this dissertation,the force and haptic feedbacktheory was studied,then the framework of the VA system based on force and haptic feedback was presented,and the functions of each module were also defined.In order to conduct research on VA technology based on force and haptic feedback,the first step is to construct VA environment.This paper turned SolidWorks models into VA models, which provided a base for further study of VA technology based on force and haptic feedback.Based on the analysis of the characters and frame of force and haptic feedback rendering algorithm,an optimization method based on collision detection was presented.In the main process,a bounding box is constructed dynamically according to the state of 3-D cursor.Then an improved oriented bounding box(OBB) collision detection method is used to reduce the untouchable triangle collections,and the remnant triangle collections are rendered in collision detection process,so the efficiency of the haptic rendering algorithm has been improved.According to the needs of wide workspace and high position resolution of VA operation using PHANTOM device,a dynamic workspace mapping method with variable parameter was also presented.In this method the proxy far from the viewpoint has larger workspace,and the proxy near the viewpoint has more accurate position precision.In order to simulate the assembly operations of the six-DOF(Degrees of Freedom) articulated robot arm in VA system,a six-DOF virtual robot arm driven by the PHANTOM device was modeled according to the structural similarity between the PHANTOM device and a six-DOF articulated robot arm.To enable the virtual robot arm to haptically interact with virtual prototypes in a virtual environment,a workspace mapping method based on robot kinematics analysis was also proposed.Based on the above-mentioned six-DOF virtual robot arm with force and haptic feedback,an assembly path planning method with virtual teaching and force feedback guiding was proposed.In this method,the guiding force is estimated using potential field method,and the virtual robot arm is driven by the PHANToM device manipulated by operator.With the help of both feedback force guideline and user's experiences and decision-making ability,the rough path planning process is being conducted in a virtual teaching way.An improved optimal method is employed to optimize the rough path.At last,the assembly process along optimized path is shown in animation,which enables users to evaluate the path and assembly process.The VA operation and navigation method based on force-feedback was explored. The assembly constraints are transformed into DOF constraints,which are reduced next.The separation problem between the proxy and parts under constraint movement was solved.Spring-damping model is employed to estimated feedback force,so the operator can feel the existence of assembly constraints.The standard tools library as well as standard fastening pars library was established,then a force-feedback-based tool interaction model was presented. The assembly sequence planning based on stability analysis was studied.By the transition from assembly constraint matrix,assembly contact matrix to assembly support matrix,the stability of each assembled parts can be analyzed.According to the stability of assembled parts,the assembly constraints and assembly direction of the unassembled parts,the parts that probably be assembled is recommended to the operator.The operator can make a decision with his/her experience on which part should be assembled.So the assembly sequence can be obtained step by step.The framework of the collaborative VA system based on force and haptic feedback using client/server structure was studied,and a contact elements prediction-based haptic rendering method was proposed.This method is conducted at both server and client side.The server predicts the basic contact elements using haptic rendering model. At client side,according to the local proxy position and basic cntact elements received from server,the finial feedback force to be sent to the PHANTOM device is estimated under the invariability assumption of contact elements.This method could not only reduce the network transfer load greatly,but also reduce the effects of both proxy position prediction error and network jitter,and the stability of the presented collaborative VA system based on force and haptic feedback were enhanced.Combining with the above-mentioned technologies,a VA prototype system based on force and haptic feedback was designed,and the assembly procedure of the power devices of a machining center was set as example to introduce process of VA design. Both the efficiency of the proposed algorithm and the feasibility of the presented VA system based on force and haptic feedback were proved.